diff --git a/AK/Hex.cpp b/AK/Hex.cpp
index a5b20057a3..e0913392f5 100644
--- a/AK/Hex.cpp
+++ b/AK/Hex.cpp
@@ -73,7 +73,7 @@ String encode_hex(ReadonlyBytes input)
     StringBuilder output(input.size() * 2);
 
     for (auto ch : input)
-        output.appendf("%02x", ch);
+        output.appendff("{:02x}", ch);
 
     return output.build();
 }
diff --git a/AK/JsonObject.h b/AK/JsonObject.h
index e3a1c6983c..57bb515f9e 100644
--- a/AK/JsonObject.h
+++ b/AK/JsonObject.h
@@ -172,7 +172,7 @@ inline void JsonValue::serialize(Builder& builder) const
         break;
 #if !defined(KERNEL)
     case Type::Double:
-        builder.appendf("%g", m_value.as_double);
+        builder.appendff("{}", m_value.as_double);
         break;
 #endif
     case Type::Int32:
diff --git a/AK/JsonObjectSerializer.h b/AK/JsonObjectSerializer.h
index 3c73c316d9..0ba6a3e47e 100644
--- a/AK/JsonObjectSerializer.h
+++ b/AK/JsonObjectSerializer.h
@@ -88,43 +88,43 @@ public:
     void add(const StringView& key, int value)
     {
         begin_item(key);
-        m_builder.appendf("%d", value);
+        m_builder.appendff("{}", value);
     }
 
     void add(const StringView& key, unsigned value)
     {
         begin_item(key);
-        m_builder.appendf("%u", value);
+        m_builder.appendff("{}", value);
     }
 
     void add(const StringView& key, long value)
     {
         begin_item(key);
-        m_builder.appendf("%ld", value);
+        m_builder.appendff("{}", value);
     }
 
     void add(const StringView& key, long unsigned value)
     {
         begin_item(key);
-        m_builder.appendf("%lu", value);
+        m_builder.appendff("{}", value);
     }
 
     void add(const StringView& key, long long value)
     {
         begin_item(key);
-        m_builder.appendf("%lld", value);
+        m_builder.appendff("{}", value);
     }
 
     void add(const StringView& key, long long unsigned value)
     {
         begin_item(key);
-        m_builder.appendf("%llu", value);
+        m_builder.appendff("{}", value);
     }
 
     void add(const StringView& key, double value)
     {
         begin_item(key);
-        m_builder.appendf("%f", value);
+        m_builder.appendff("{}", value);
     }
 
     JsonArraySerializer<Builder> add_array(const StringView& key)
diff --git a/AK/LogStream.cpp b/AK/LogStream.cpp
index 08da5f705b..7837050e42 100644
--- a/AK/LogStream.cpp
+++ b/AK/LogStream.cpp
@@ -207,9 +207,9 @@ void dump_bytes(ReadonlyBytes bytes)
     auto flush = [&]() {
         if (nrepeat > 0) {
             if (nrepeat == 1)
-                builder.appendf("%s0x%02x", prefix, static_cast<int>(buffered_byte));
+                builder.appendff("{}{:#02x}", prefix, static_cast<int>(buffered_byte));
             else
-                builder.appendf("%s%zu * 0x%02x", prefix, nrepeat, static_cast<int>(buffered_byte));
+                builder.appendff("{}{} * {:#02x}", prefix, nrepeat, static_cast<int>(buffered_byte));
 
             nrepeat = 0;
             prefix = ", ";